The present invention relates to a silencer in a refrigeration system for silencing a jet noise produced as a result of an adiabatic expansion of refrigerant in a restriction constituting a pressure reducing device of the refrigeration system of a room air conditioner, refrigerator, automobile air conditioner or the like.
In the room air conditioners, refrigerators, automobile air conditioners or the like having a refrigeration system incorporating a fixed restriction or a capillary tube constituting a pressure reducing device, a jet noise of a high level is generated due to an adiabatic expansion of the refrigerant at the outlet side of the pressure reducing device and due to a drastic increment of the cross-sectional area of the refrigerant pipe. The level of the jet noise becomes higher as the pressure difference or pressure drop of the refrigerant across the restriction becomes greater. Particularly, in the case where the refrigeration system operates discontinuously or by an on-off control, the gaseous refrigerant in the two-phase flow of refrigerant makes a rapid adiabatic expansion to periodically produce large noise. It has been confirmed that this jet noise is maximized immediately after the stopping or starting of the compressor.
This jet noise imparts quite an unpleasant feel to the user, and there is an increasing demand for eliminating or suppressing this jet noise.
Generally, as to the jet noise produced by a fluid jetted from a nozzle or the like, the following phenomenon are observed. A so-called jet core of an equal potential energy level is distributed in the region of a distance 4D (D represents the diameter of nozzle) from the nozzle. This region is generally referred to as mixing region. As the fluid is jetted, numerous eddy currents are formed in the boundary between the mixing region of the jet and the ambient fluid, to generate a noise of a high frequency. Also, a noise of low frequency is generated in the boundary region between the mixing region and a region of turbulent flow formed at the downstream side of the mixing region. It is considered that the noise energy is distributed making this boundary region substantially as a center.
This characteristic of jet noise applies also to the jet noise generated in the restriction of refrigerant passage in the refrigeration system. Particularly, the high frequency noise generated in the mixing region imparts an unpleasant feel.